In a CCL use copper foil, when bonding the copper foil to a resin substrate, it is necessary to improve its bonding strength and satisfy required electrical property, etching property, heat resistance, and chemical resistance as a printed circuit board. For this reason, roughening treatment is applied to the bonding surface of the copper foil to be bonded with the resin substrate after the foil is produced (hereinafter sometimes described as the “untreated copper foil”), further zinc (Zn) plating, nickel (Ni) plating, or the like is applied to the top of the roughened surface, still further chromate treatment etc. are applied to the top of the surface plated with the Zn, plated with the Ni, and a variety of other techniques are applied.
Recently, IC mounted boards driving liquid crystal displays of display parts of PCs, mobile phones, and PDAs are becoming increasingly advanced in density. In the production processes thereof accurate circuit configurations and a treatment at a high temperature are demanded.
To respond to such demands, as a copper clad laminate for producing printed circuit boards, for a response to demands for accurate circuit configurations and treatment at a high temperature, a CCL is provided in which an electrodeposited copper foil capable of forming accurate conductive circuits and a polyimide film which is resin substrate capable of being used at a high temperature are bonded together. In the CCL, the copper foil and the polyimide are bonded by thermal adhesion at high temperature of several hundreds of degrees.
For this bonding treatment at the high temperature, improvement of the bonding strength of the copper foil with the polyimide film has become the pressing issue. As a means for solving this problem, the technique of roughening treatment of the surface of the copper foil by a Zn-containing alloy is disclosed in for example PLT 1.
Further, as a means for bonding a copper foil and a polyimide film at a high temperature, a surface treated copper foil obtained by treating the surface of untreated copper foil for bonding with a polyimide film by an electroplating solution containing at least one element selected from among molybdenum, iron, cobalt, nickel, and tungsten and further providing a Ni plating layer or Zn plating layer or else a Ni plating layer plus a Zn plating layer on this plating layer has been proposed (see PLT 2).
The roughened layer including a Zn layer disclosed in the above PLT 1 and PLT 2 has an advantageous effect in the point that the bonding strength between the copper foil and the polyimide film (resin substrate) at a high temperature is improved. However, if forming a conductive circuit by etching treatment by an acidic solution after bonding the copper foil to the polyimide film (resin substrate) and constituting a circuit board, even the Zn layer which bonds the copper foil and the polyimide film (resin substrate) begins to dissolve since zinc is easily dissolved by acid, so there is apprehension that the bonding strength between the copper foil and the polyimide film (resin substrate) after forming the circuit will sharply fall and accidents of the conductive circuit peeling off from the polyimide film (resin substrate) during use of the circuit board will occur. In order to prevent such accidents, it was necessary to shorten the etching time and keep the dissolution and outflow of the Zn layer to the lowest limit, therefore advanced technology and management systems were needed for the etching treatment, so there were the disadvantages that the productivity of the circuit boards was reduced and costs became higher.
In this way, with the roughening treatment of copper foil disclosed in the above PLT 1 and PLT 2, as described above, the bonding strength with respect to the polyimide film, chemical resistance, and etching property could not be all satisfied. And in the present state, a surface treated foil satisfying all of them has never been provided.
Furthermore, a CCL satisfying all of the bonding strength, chemical resistance, and etching property has never been provided.
And in the PLT 3, as a surface treatment of a copper foil, Ni—Zn plating is performed using pyrophosphoric acid bath for plating bath, and CCL comprised of the surface treated copper foil and polyimide film is proposed. It is disclosed that by using the pyrophosphoric acid bath, Ni—Zn alloy layer being excellent in film thickness uniformity is obtained, and the phenomenon of penetration of tin into the interface between the circuit and the polyimide resin substrate is hard to occur when the tin plating is performed to the terminal area after the circuit is formed.
However, in the plating using the pyrophosphoric acid bath, it is known that P is codeposited in the plated coating, which has property of high solubility due to the codeposited P. According to that property, when the copper foil is etched to form a circuit and tin plating is performed on the terminal area of thus formed circuit, the phenomenon of penetration of tin plating solution (deterioration of chemical resistance) is not able to be prevented sufficiently, the surface treated layer is deteriorated by the tin plating solution, and there is a failure that an influence happens on the adhesion property of wiring circuit.
In recent years, the pitch of the circuit is becoming finer and the width of wiring circuit is becoming finer, and bonding area between the circuit and the resin substrate is decreasing. In such a fine pitch circuit, when the phenomenon of penetration of tin plating solution occurs, the adhesion property of circuit deteriorates and a problem of reliability occurs, therefore a copper foil is desired which is capable of suppressing this phenomenon of penetration of tin plating solution.